MY 99 Montana won't rev past 3000 rpm's

When I have the car in park and rev the engine it won't rev past 3000 rpm's. When I drive the car it runs great until I need it to go past 3000 rpm's. It struggles and then pushes back to 3000 rpm's. I thought it might be the MAF sensor, but I was told that it you unplug it and the problem still continues then it's not the sensor. I tried that and it still has the problem. Is there anyone that has any Idea what the problem might be?